Syringe pump

ABSTRACT

THE MOTORS FOR THE SEPARATELY RECIPROCATING DRIVE MECHANISMS OF A TWO BARREL SYRINGE PUMP ARE PROVIDED WITH ELECTRIC CONTROL CIRCUITS AND SWITCHES WHICH ARE ACTUATED BY THE RECIPROCATING DEVICE MECHANISMS AND WHICH CAUSE A FULLY WITHDRAWN SYRINGE TO COMMENCE INFUSION JUST BEFORE THE OTHER SYRINGE COMPLETES INFUSION, THE SWITCHES   ALSO CAUSING SOLENOID VALVE MEANS TO OPERATE IN PHASED RELATION TO THE INFUSION OF THE SYRINGES WHEREBY THE INFUSION IS CARRIED OUT AT A CONSTANT RATE WITHOUT PERCEPTIBLE INTERRUPTIONS OR SURGES WHEN THE INFUSION OF FLUID CHANGES OVER FROM ONE SYRINGE TO THE OTHER AND BACK AGAIN.

;J an-.u 12, A1971y M; scHwA-rz'. EI'AL '3,554,673

' `V`SYRINGE: -PUMP Filed Jan. ,311, 1969 2 Sheets-Sheet 1 Urt.:

FIG. 1

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FIG. 3

INVENTQRS JOEL M. SCHWARTZ BY DANIEL F. KREBs 'nomnzvs SYRINGE PUMP 2Sheets-Sheet 2 ENV v moSz/EN IOPOE CNN INVO- INVENTORS JOEL M. SCHWARTZDANIEL F. KREBS United States Patent O 3,554,673 SYRINGE PUMP Joel M.Schwartz, White Plains, and Daniel F. Krebs, Yonkers, N Y., assignors toSage Instruments, Inc., White Plains, N.Y., a corporation of New YorkFiled Jan. 31, 1969, Ser. N0. 795,572 Int. Cl. F04b 7/00, 17/00 U.S. Cl.417-412 4 Claims ABSTRACT OF THE DISCLOSURE The motors for theseparately reciprocating drive mechanisms of a two barrel syringe pumpare provided with electric control circuits and switches which areactuated by the reciprocating drive mechanisms and which cause a fullywithdrawn syringe to commence infusion just before the other syringecompletes infusion, the switches also causing solenoid valve means tooperate in phased relation to the infusion of the syringes whereby theinfusion is carried out at a constant rate without perceptibleinterruptions or surges when the infusion of fluid changes over from onesyringe to the other and back again.

BACKGROUND OF THE INVENTION (l) Field of the invention This inventionrelates to syringe pumps, and more particularly to two barrel syringepumps designed to continuously infuse the iluid being pumped at aconstant, predetermined rate.

(2) Prior art A typical syringe pump comprises a syringe and areciprocating drive mechanism for moving the plunger of the syringeforwards and backwards within the barrel f the syringe. The syringe isconnected by appropriate tubing and valves to a source of reservoir ofthe fluid being pumped and to the body or other object to which thefluid is being delivered. Movement of the syringe plunger away from thefluid opening at the bottom of the syringe barrel withdraws fluid fromthe fluid reservoir (hereinafter referred to as the withdrawal phase ofoperation of the pump) and movement of the syringe plunger toward thefluid opening of the syringe barrel delivers fluid to the body or otherobject (hereinafter referred to as the infusion phase of operation ofthe pump). The syringe of a syringe pump is usually removable so that itcan be cleaned or replaced by a syringe of a different size. Such pumpsprovide uniform, accurate and reproducible infusion of fluids and areuseful in a wide range of applications in analytical, medical,biological and industrial areas.

When the syringe pump comprises only one syringe and drive mechanism,the infusion of the fluidT by the pump is interrupted when the syringeplunger reaches the bottom of the syringe barrel, and infusion cannot beresumed until the plunger has been withdrawn and the syringe barrelrefilled. Continuous infusion can be obtained by the use of two syringesoperated by separate drive mechanisms, the infusion and withdrawalphases of the two syringes being staggered so that one syringe willalways be infusing while the other syringe is withdrawing and refilling.Although such double acting, two barrel syringe pumps are capable ofsubstantially continuous infusion, there can be a short but perceptibleinterruption in the infusion of fluids, or even a reversal in thedirection of flow of the fluid being infused, when one syringe stopsinfusion, or even starts to withdraw, before the other syringe commencesinfusion.

It has heretofore been proposed to avoid the interruption, andespecially the momentary reversal in direction,

Patented Jan. 12, 1971 ICC of the fluid being infused by providingmechanically operated valve means for the inlet and outlet tubes of thesyringes of a two barrel syringe pump which delay the opening of theoutlet tube of the syringe just beginning its infusion phase until thissyringe has built up sucient pressure to overcome the back pressure inthe infusion line 0f the pump. However, as the other syringe isbeginning its withdrawal phase of operation the valve means for theoutlet tubing of the latter syringe must be closed before the outletvalve of the first syringe is opened. As a result, a perceptibleinterruption in the infusion of liquid remains.

After an intensive investigation into the problems involved in thedesign of a syringe pump capable of infusing a fluid at a constant,controlled rate without interruptions or perceptible fluctuations in therate of delivery of fluid when the infusion of one syringe stops andthat of the other commences, we have discovered that a two barrelsyringe pump capable of meeting these requirements must carry outalternate infusion and withdrawal phases in a prescribed and criticalsequence of operational steps. Specifically, we have found that a fullywithdrawn and filled syringe must start infusion before the othersyringe completes its infusion phase of operation. Moreover, the closureof the inlet valve and the opening of the outlet valve of the rstsyringe Imust be delayed until after this syringe has commenced infusionso that, momentarily at least, the lirst syringe isvpumping back to thefluid reservoir. Finally, we have found that the opening of the outletvalve of the first syringe and the closure of the outlet valve of thesecond syringe must take place at essentially the same moment.

SUMMARY OF THE INVENTION The improved syringe pump of our invention isadapted to carry out the aforementioned essential sequence ofoperational steps and comprises, in its basic components, two syringeseach adapted alternately to infuse and to withdraw a fluid being pumped,a reciprocating drive mechanism for each syrin-ge and valve means foralternately opening and closing the fluid inlet and fluid outlet linesof each syringe in operational relationship with respect to the infusionand withdrawal phases of operation of syringes. Separately controlledeelctric motors are connected to each drive mechanism in our improvedstructure, and first and second motor control means actuated by thereciprocating drive mechanisms are provided for operating each of theseparately controlled Imotors. Each motor control means is adapted tocomplete the withdrawal phase and start the infusion phase of operationof the motor to which it is connected before the other motor completesits infusion phase and starts to withdraw fluid.

In the preferred embodiment of our invention each motor control meanshas a controlled infusion circuit for operating the motor to which it isconnected in the direction of fluid infusion at a controlled variablespeed and a rapid withdrawal circuit for operating the motor in thedirection of fluid withdrawal at a higher speed than the maximum speedof fluid infusion. The valve means cornprise first solenoid means forsimultaneously closing the inlet of the first of the two syringes andthe outlet of the second of the two syringes, and second solenoid meansfor simultaneously closing the outlet of the rst syringe and the 'inletof the second syringe. Each motor control includes electric switch meansactuated by the reciprocating drive mechanisms when the drive mechanismsreach each end of their reciprocating paths of travel, the switch meansbeing connected to the controlled infusion circuits and to the rapidWithdrawal circuits of the first and second motor control means andbeing connected to the Ifirst and second solenoid means.

In accordance with our invention, the drive mechanism for the firstsyringe causes the switch means to energize the controlled infusioncircuit of the second motor control before de-energizing the controlledinfusion circuit of the first motor control and before energizing thesecond solenoid means when said first drive mechanism reaches the end ofits controlled infusion direction of travel. In like manner, the drivemechanism in the second syringe causes the switch to energize thecontrolled infusion circuit of the first motor control beforedeenergizing the controlled infusion circuit of the second motor controland before energizing the first solenoid means when said second drivemechanism reaches the end of its controlled infusion direction oftravel.

BRIEF DESCRIPTION OF THE DRAWINGS The improved syringe pump of ourinvention will be better understood from the following descriptionthereof in conjunction with the accompanying drawings of which FIG. l isa plan view, partly broken away, of an advantageous embodiment of thetwo-barrel syringe pump of our invention.

FIG. 2 is a side elevation, partly broken away, of the syringe pumpshown in FIG. l,

FIG. 3 is a schematic diagram of the fluid tubing layout of the pumpshown in FIG. l, and

F-IG. 4 is a schematic diagram of an electrical circuit adapted to carryout the essential sequence of operations characteristic of the improvedsyringe pump of our invention.

DETAILED DESCRIPTION The embodiment of the syringe pump of our inventionshown in FIGS. l and 2 of the drawing comprises a housing having a topplate 11 on which most of the operating elements of the syringe pump aremounted. Adjustable syringe holders 12 and 13 are mounted on the topplate 11, each syringe holder being adapted to hold a syringe 14 and 15as indicated by the dotted lines in FIGS. 1 and 2. The holders 12 and 13are adjustable so that syringes of various sizes can be mounted therein,the syringes 14 and 15 preferably being substantially identical in size.Separately controlled drive mechanisms 16 and 17 are mounted on the topplate 11, each drive mechanism being adapted to move the plunger of oneof the syringes backwards and forwards in a reciprocating path oftravel. Also mounted on the top plate 11 are solenoid operated valvemeans 18 for opening and closing the inlet and outlet lines of thesyringes 14 and 15 as required for the proper operation of the syringepump. A power line 19 and fuse holder 20 are mounted on one side of thehousing 10, and the main on-off switch 21 and pilot light 22 are mountedon the other side of the housing. Also mounted on the housing are thevariable speed controls (i.e., rheostats) 23 and 24 for the drivemechanisms 16 and 17 of the device.

In the embodiment shown in the drawing, the drive mechanisms 16 and 17have separately reciprocating drive carriages 26 and 27 to which theplungers 28 and 29 of syringes 14 and 15 are secured by adjustableplunger clamps 30 and 31. The drive carriages 26 and 27 each comprise abox-like structure having a longitudinal extending rack 32 and 33t,respectively, which are engaged by drive pinions 34 and 35,respectively. Idler gears 36 and 37 are disposed on the other side ofeach drive carriage 26 and 27. As shown in FIG. 2, the drive pinion ofdrive carriage 27 is driven through a reduction gear train 39 by areversible, variable speed motor 41. The drive pinion 34 of drivecarriage 26 is driven through a similar reduction gear train 38 andreversible, variable speed motor 40 that cannot be seen in the drawing.

The reversible, variable speed motors 40 and 41 are each connected tomotor control means which operate the motor associated therewith at acontrolled variable speed when the motor is moving the drive carriagedriven thereby in the direction of fluid infusion, the motor controlmeans having a controlled infusion speed circuit for this purpose. Eachmotor control means also operates the motor associated therewith at aconstant rate of speed that is higher than the maximum rate of speedthat is higher than the maximum rate of speed in the direction ofcontrolled infusion when the motor is moving the drive carriage in thedirection of uid withdrawal, the motor control means having a rapidwithdrawal speed circuit for this purpose. The controlled infusioncircuits (which include the rheostats 23 and 24) and the rapidwithdrawal circuits of the motor control means are conventional and arenot described in detail herein. The motor control means for the motors40 (not visible in the drawing) and 41 also include lever switches 42(not visible in the drawing) and 43 which are operated by thereciprocating drive carriages 26 and 27, respectively, when these drivecarriages reach each end of their reciprocating paths of travel. To thisend, the drive carriage 26 is provided with adjustable limit stops 44and 45 which alternately contact and move the lever 46 of the leverswitch 42, and the drive carriage Z7 is provided with adjustable limitstops 47 and 48 which alternately contact and move the lever 49 of thelever switch 43, when the drive carriages reach each end of theirreciprocating paths of travel.

The solenoid operated valve means 18 comprises a valve anvil 50 formedwith two pairs of transverse slots 51 and 52 adapted to receive theinlet and outlet lines or tubing of the syringes 14 and 15 and with alongitudinal slot 53 adapted to receive two plate-like valve members 54and 55. The valve member 54 is positioned in the longitudinal slot 53directly above the tubing disposed in the pair of transverse slots 51,and the valve member 55 is disposed in the slot 53 directly above thetubing disposed in the pair of slots 52. Moreover, the valve member 54is connected to the armature 56 of a solenoid 57 so that when thesolenoid is energized the tubes received in the slots 51 will besqueezed shut and when the solenoid 57 is deenergized the tubingreceived in the slots 51 will reopen. Similarly, the valve member 55 isconnected to the armature 58 of a solenoid (not visible in the drawing)which when energized and de-energized cause the tubing received in thepair of slots 55 to be closed and reopened.

The arrangement of the elastomeric inlet and outlet tubing of the twosyringes 14 and 15 is shown in FIG. 3. The inlet tube `62 for syringe 14extends through one of the slots 51 underlying the valve member 54 tothe main uid withdrawal line 63 that is connected to the source of fluidbeing pumped, and the outlet tube 64 for syringe 14 extends through oneof the slots 452 underlying the valve member 55 to the main fluidinfusion line 65 that is connected to the object to which fluid is beingdelivered. Similarly, the inlet tube 66 of syringe 15 extends throughthe other of the slots 52 underlying the valve member 55 to the fluidwithdrawal line 63. and the outlet tube 67 of syringe 15 extends throughthe other of the slots 51 underlying the valve member 54 to the uidinfusion line 65. Thus, when the solenoid 57 connected to the valvemember 54 is energized the inlet tube 62 of syringe 14 and the outlettube 67 of syringe 15 will be closed, and when the solenoid connected tothe valve member 55 is energized the outlet tube 64 for the syringe 14and the inlet tube 66 for syringe 15 will be closed. Alternateenergizing and deenergizing of the solenoids in operational relationshipwith the infusion and withdrawal phases of operation of the syringes 14and 15 will permit continuous uninterrupted infusion of the lluid beingpumped.

The switch means 42 and 43 are connected through appropriate electricalcircuitry to the controlled infusion circuits and to the rapidwithdrawal circuits of the motor controls for the motors 40 and 41, andalso to the solenoids which actuate the valve members 54 and 55 of thesolenoid valve 18. The specific circuitry employed may include relays,printed circuit cards, and/or solid state components in lany suitablecombination provided the circuitry is adapted to carry out the essentialsequence of operational steps that are characteristic of our improvedsyringe pump. Specifically, the circuitry should cause the followingsequence of electrical operations to be carried out when thereciprocating drive carriages 26 and 27 contact the lever switches 42and 43 when the drive carriages reach each end of their reciprocatingpaths of travel. p

(l) After the drive carriage 26 reaches its fully infused position: therapid withdrawal circuit of the motor control for motor 40 is energized,the solenoid for valve member 54 is de-ener-gized, and the solenoid forvalve member 55 is energized;

(2) When the drive carriage 26 reaches its fully withdrawn position: therapid withdrawal circuit of the motor control for motor 40 isde-energized;

(3) As the drive carriage 27 approaches its -fully infused position: thecontrolled infusion circuit of the motor control for motor 40 isenergized;

(4) After the drive carriage 27 reaches its fully infused position: therapid withdrawal circuit of the motor control for motor 41 is energized,the solenoid for valve member 54 is energized, and the solenoid forvalve member 55 is de-energized;

(5) When the drive carriage 27 reaches its fully withdrawn position: therapid withdrawal circuit of the rnotor control for motor y41 isrie-energized;

(6) As the drive carriage 26 approaches its fully infused position: thecontrolled infusion circuit of the motor control for motor 41 isenergized;

The foregoing sequence of electrical operations cause the followingsequence of functional steps to take place:

right contact 109 also energizes the rapid withdrawal motor control 115of the motor 116 (which corresponds to motor previously referred to),thereby causing the drive carriage 26 of the pump shown in FIG. l tomove rapidly to the fully withdrawn position of the carriage. Currentfrom the now closed contact 208 of switch 206 energizes the controlledinfusion motor control 217 of the motor 216 (which corresponds to motor41), thereby causing the drive carriage 27 of the pump shown in FIG. 1to move at a controlled rate toward the fully infused position of thecarriage. Current from the now closed contact 213 of switch 211energizes the solenoid valve 218 (which corresponds to the valve means55 shown in FIG. 3), thereby closing outlet tube 64 of the syringe 14and inlet tube 66 of syringe 15. Current from the upper left contact 219of lever switch 204 flows to the now closed contact 207 and through theholding circuit of switch 206, and current from the normally closedcontact 114 of switch 111 flows to the now closed contact 212 andthrough the holding circuit of switch 211. Finally, current from thelower left contact 220 energizes the coil of solenoid switch 221,thereby opening the normally closed contact 222 of switch 221. All ofthese actions take place more or less instantaneously when the switch101 is closed.

When the rapidly withdrawing drive carriage 26 reaches its fullywithdrawn position it contacts the lever 103 of lever switch 104 andmoves it from the position shown in solid lines to the position shown indotted lines in FIG. 4, thereby opening right contacts 105 and 110 andclosing left contacts 119 and 120 of switch 104. The opening of rightcontacts 105 and 110 does not de-energize the coils of solenoid switches206 and 211 because the holding circuits of these switches areenergized, and the ped d do do o Controlledinfusion do Do.

An electrical circuit that is adapted to carry out the essentialseqeunce of operational steps characteristic of the syringe pump of ourinvention is shown in FIG. 4 of the drawing. However, the circuit sho-wnin FIG. 4 is merely illustrative of one such circuit and our inventionis not limited thereto. Other circuits employing other types of leverswitches, relays, printed circuit cards, solid state components and thelike can readily be devised which will effect the desired sequence ofoperations of our two barrel syringe pump. Y

Referring now to FIG. 4, assume that the pump is turned off when one ofthe syringes of the pump is in the middle of the withdrawal phase of itscycle and the other syringe of the pump is in the middle of the infusionphase of its cycle of operation. lIn this situation, the main switch 101Will be open, the pilot light 102 will be out and the levers 103 and 203of the lever switches 104 and 204 will be in the positions shown in FIG.4 of the drawing.

When the switch 101 is closed, the pilot light 102 lights up and currentflows to the lever switches 104 and 204 and through the circuitsassociated therewith. Specifically, current from upper right contact 105of lever switch 104 energizes the coil of solenoid switch 206, therebyclosing the normally open contacts 207 and 208 and opening the normallyclosed contact 209 of switch 206. Current from lower right contact 110of lever switch 104 energizes the coil of solenoid switch 211, therebyclosing the normally open contacts 212 and 213, and opening the normallyclosed contact 214 of switch 211. Current from the lower opening oflower right contact does not de-energize the withdrawal motor controlbecause contacts 114, 212 and 122 of switches 111, 211 and 121 areclosed. The closing of upper left contact 119l energizes the normallyopen contact 107 of switch 106. The closing of lower left contact 120energizes the coil of solenoid switch 121, thereby opening normallyclosed contact 122 and thus de-energizing the withdrawal motor control115.

When the rapidly withdrawing drive carriage 26 reaches its fully infusedposition it contacts the lever 203 of lever switch 204 and moves it fromthe position shown in solid lines to the position shown in dotted linesin FIG. 4. As the lever 204 moves from left to right it first openslower left contact 220, thereby de-energizing solenoid switch 221 andclosing contact 222. The lever 203 then contacts the arcuate extensionof upper right contact 205 which energizes the coil of solenoid switch106, thereby closing the normally open contacts 107 and 108 and openingthe normally closed contact 109 of the switch 106. Closure of contact107 energizes the holding circuit of switch 106. Closure of contact 108`energizes the controlled infusion motor control 17 of the motor 116,thereby causing the drive carirage 26 of the pump to start to move at acontrolled rate toward the fully infused position of the carriage. Themoving lever 203 then opens the arcuate extension of upper left contact219 of switch 204 which de-energizes the holding circuit of solenoidswitch 206, thereby opening contacts 207 and 208 and closing contact 209of switch 206. The opening of contact 208 de-energizes the controlledinfusion motor control 217 thereby causing the motor 216 to stopinfusion. The lever 203 then contacts the lower right contact 210 whichenergizes the rapid withdrawal motor control 215 of the motor 216 andalso the coil of solenoid switch 111.

Energizing of switch 111 closes normally open contacts 112 and 113 andopens normally closed contact 114. Closure of contact 113 energizessolenoid valve 118 (which corresponds to the valve means 54 shown inFIG. 3), thereby closing the inlet tube 62 of syringe 14 and the outlettube 67 of syringe 15. Opening7 of contact 114 de-energizes the holdingcircuit of switch 211, thereby opening contacts 212 and 213 and closingcontact 214 of switch 211. Opening of contact 213 de-energizes solenoidvalve 218, thereby opening the inlet tube 66 of syringe and the outlettube 64 of syringe 14. Closure of contact 214 energizes the holdingcircuit of switch 111. The commencement of the rapid withdrawal phase ofoperation of motor 216 and the associated syringe 15, the closure ofsolenoid valve 118 and the opening of solenoid valve 218 take placeessentially simultaneously.

The drive carriage 26 of the syringe 14 moves at a controlled,relatively slow rate toward the fully infused position of the carriagewhile the drive carriage 27 of the syringe 15 moves relatively to thefully withdrawn position of the carriage. When the rapidly moving drivecarriage 27 reaches its fully withdrawn position it moves the lever 203of lever switch 204 from right to left, thereby de-energizing the rapidwithdrawal motor control 215 and stopping the motor 216. The drivecarriage 26 of the syringe 14 continues in the meantime to move at acontrolled rate toward its fully infused position. When the drivecarriage 26 reaches its fully infused position it moves the lever 103 oflever switch 104 from left to right,

thereby sequentially energizing the controlled infusion g motor control217, then de-energizing the controlled infusion motor control 117, andthen essentially simultaneously energizing the rapid withdrawal motorcontrol 115, energizing the solenoid valve 218 and de-energizing thesolenoid valve 118. When the rapid withdrawal motor control 115 andmotor 116 move the drive carirage 26 to its fully withdrawn position thelever 103 will be moved from right to left, and when the controlledinfusion motor control 217 and motor 216 move the drive carriage 27 toits fully infused position the lever 203 will be moved from left toright, thereby effecting the sequences of operations previouslydescribed. The cyclic operation of the syringe pump continues in themanner described until the main switch 101 is opened.

As noted, the specific drive mechanism and the electrical circuitryassociated therewith herein described comprise an advantageous, but byno means the only, means of carrying out the cyclic sequence ofoperations characteristic of the syringe pump of our invention. Forexample, the desired series of operational steps could be carried out bythe use of a single electric motor which runs in one direction only andwhich is provided with a variable speed control. In this embodimentgears would be switched in and out of engagement by means of solenoidsand clutches operated by the switch means of the apparatus. The solenoidoperated gears and clutches would be adapted to change the direction oftravel of the drive carriage and to control the speed of infusion andwithdrawal so that withdrawal is always faster than infusion. Otherdrive mechanisms adapted to carry out the required sequence ofoperational steps characteristic of our syringe pump could be devised.

In addition to the use of our syringe pump to continuously infuse asingle iiuid into an object or body, the syringe pump of our inventioncan be employed as a proportioning pump. In this application the intakeline of each syringe is connected to a separate fluid supply reservoir.In operation, fluid withdrawn alternately from each fluid supplyreservoir would be infused sequentially into the object or body to whichthe uid is being delivered.

The amount of fiuid infused into the body by each syringe of the pump iscontrolled by adjustment of the stroke length and selection of syringesize.

We claim:

1. In a syringe pump comprising two syringes each adapted alternately toinfuse and to withdraw a fluid being pumped, a reciprocating drivemechanism for each syringe and valve means for alternately opening andclosing the fluid inlet and fiuid outlet lines of each syringe inoperational relationship with the infusion and withdrawal phases ofoperation of said syringes, the improvement which comprises:

a separately controlled electric motor connected to each drivemechanism,

first and second motor control means actuated by the reciprocating drivemechanisms for operating each of said separately controlled motors, eachmotor control means having a controlled infusion circuit for operatingthe motor to which it is connected in the direction of fluid infusion ata controlled variable speed and a rapid withdrawal circuit for operatingsaid motor in the direction of fluid withdrawal at a higher speed thanthe maximum speed of iiuid infusion,

valve means comprising first solenoid valve means for simultaneouslyclosing the inlet of the first of the two syringes and the outlet of thesecond of the two syringes, and second solenoid valve means forsimultaneously closing the outlet of the first syringe and the inlet ofthe second syringe, and

electric switch means for the controlled infusion circuits and the rapidwithdrawal circuits of the first and second motor control means and forthe first and second solenoid valve means, said switch means beingactuated by the reciprocating drive mechanisms when the drive mechanismsreach each end of their reciprocating paths of travel.

2. The syringe pump according to claim 1 in which the drive mechanismfor the first syringe causes the switch means to energize the controlledinfusion circuit of the second motor control before de-energizing thecontrolled infusion circuit of the first motor control and beforeenergizing the second solenoid means when said first drive mechanismreaches the end of its controlled infusion direction of travel, and inwhich the drive mechanism for the second syringe causes the switch meansto energize the controlled infusion circuit of the first motor controlbefore de-energizing the controlled infusion circuit of the second motorcontrol and before energizing the first solenoid means when said seconddrive mechanism reaches the end of its controlled infusion direction oftravel.

3. The syringe pump according to claim 1 in which the switch means (a)energizes the controlled infusion circuit of the second motor controlbefore de-energizing the controlled infusion circuit of the first motorcontrol, and then energizes the second solenoid means and the rapidwithdrawal circuit of the first motor control and de-energizes the firstsolenoid means, when said first drive mechanism reaches the end of itscontrolled infusion direction of travel, (b) de-energizes said firstrapid withdrawal circuit when said first drive mechanism reaches the endof its rapid withdrawal direction of travel, (c) energizes thecontrolled infusion circuit of the first motor control beforede-energizing the controlled infusion circuit of the second motorcontrol, and then energizes the first solenoid means and the rapidwithdrawal circuit of the second motor control and de-energizes thesecond solenoid means, when said second drive mechanism reaches the endof its controlled infusion direction of travel, and (d) de-energizessaid second rapid withdrawal circuit when said second drive mechanismreaches the end of its rapid withdrawal direction of travel.

4. The syringe pump according to claim 1 in which the reciprocatingdrive mechanisms for the first and second syringes cause the switchmeans to effect the following sequence of electrical operations:

(a) as the first drive mechanism approaches its fully infused position:controlled infusion circuit of second motor control energized;

(b) after the irst drive mechanism reaches its fully infused position:rapid Withdrawal circuit of first motor control energized, firstsolenoid means de-ener gized, and second solenoid means energized;

(c) when the irst drive mechanism reaches its fully withdrawn position:rapid Withdrawal circuit of first motor control de-energized;

(d) as the second drive mechanism approaches its fully infusedposition:controlled infusion circuit of first motor control energized;

I (e) after the second drive mechanism reaches its fully infusedposition: rapid withdrawal circuit of second motor control energized,rst solenoid means energized, and second solenoid means de-energized;

(f) when the second drive mechanism reaches its fully withdrawnposition: rapid Withdrawal circuit of second motor control de-energized.

References Cited UNITED STATES PATENTS 2,419,993 5/1947 Green et al103-152 10 3,259,077 7/1966 Wiley et al 103-227 ROBERT M. WALKER,Primary Examiner U.S. C1. X.R. 15 417-515 gjg t UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,554 ,673 DatedJantla'ry`l2L 1971 lnvcntods) Joel M. Schwartz and Dan'el P. Krel'ns It:ls certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- Column 1 llne. 39,' "of" should read or --v r Column 1, 1ne.55, "ofthe should read o'vf cu; Columm 2, line 4S; l "',eelectrid should readelectric Column 3., Alne, "longitudinal" lshould n read 'lo'ngtixdna.Column 4,- 1ines 7 and 8, "that is h'irgher than the maximum t rate ofspeed" is repeated and the second -occurence should be deleted.

Coluxrn 5, line 47, "electrical" should' readllelectric Column1 6, lineSS', "when the rapidly vrthdrawng drive. carriage 26" should read 4whenthe moreslowljr moving drive carrageZ? Column 6, line 68', "1 7" shouldread 117 ;l

'Column 7. `1ine 25. "relatively to" should red relatively rapidly toColumn 7, l'ne 41, "carirage" sho'uld read ca rrage Signed and sealedthis 11th day of May" 1971 (SEAL) Attest: l EDWARD mrmamcfum,Jn.lWILLIAM E. scHUYLER Jn. Attesting officer cummiasioner or Patnca.

